const epsilon = 1e-6;

export default class Path {
  constructor() {
    this._x0 = this._y0 = // start of current subpath
    this._x1 = this._y1 = null; // end of current subpath
    this._ = "";
  }
  moveTo(x, y) {
    this._ += `M${this._x0 = this._x1 = +x},${this._y0 = this._y1 = +y}`;
  }
  closePath() {
    if (this._x1 !== null) {
      this._x1 = this._x0, this._y1 = this._y0;
      this._ += "Z";
    }
  }
  lineTo(x, y) {
    this._ += `L${this._x1 = +x},${this._y1 = +y}`;
  }
  arc(x, y, r) {
    x = +x, y = +y, r = +r;
    const x0 = x + r;
    const y0 = y;
    if (r < 0) throw new Error("negative radius");
    if (this._x1 === null) this._ += `M${x0},${y0}`;
    else if (Math.abs(this._x1 - x0) > epsilon || Math.abs(this._y1 - y0) > epsilon) this._ += "L" + x0 + "," + y0;
    if (!r) return;
    this._ += `A${r},${r},0,1,1,${x - r},${y}A${r},${r},0,1,1,${this._x1 = x0},${this._y1 = y0}`;
  }
  rect(x, y, w, h) {
    this._ += `M${this._x0 = this._x1 = +x},${this._y0 = this._y1 = +y}h${+w}v${+h}h${-w}Z`;
  }
  value() {
    return this._ || null;
  }
}